This is a cranial X-ray of an individual who tried to commit suicide with a crossbow, and who sustained damage to the ventromedial prefrontal cortex in the process. Prior to the suicide attempt, he had been diagnosed with antisocial personality disorder (APD), a condition which is characterized by impulsive behaviour and an indifference to social norms and the feelings and rights of others. The patient exhibited personality changes after the injury, but not in the way one might expect – his antisocial behaviour ceased.
The link between the frontal lobes and social behaviour dates back at least 150 years, to John Harlow’s descriptions of the injuries incurred by Phineas Gage, and the ensuing personality changes. The history of neurology is peppered with case studies of individuals such as Gage. Clinical observations of these patients have enabled neurologists to localize behaviours to specific regions of the cerebral cortex (but this smacks of phrenology, and in reality, things are not so simple). Consequently, it is now relatively well established that the frontal lobes are involved in social cognition, as these processes are often impaired as a result of damage to this region of the brain.
The X-ray image above comes from a 2006 paper cited in an essay called Law, Responsibilty and the Brain, which is published online today in PLoS Biology. The authors, from the Wellcome Trust Centre for Neuroimaging at UCL, briefly review how damage to various parts of the frontal or temporal lobe is correlated with anti-social behaviour patterns. To summarize, frontal lobe damage is now generally assumed to result in “acquired sociopathy” – it is associated with increased aggression or violence and, sometimes, changes in sexual behaviour. On the other hand, damage to the amygdala, a structure found on the medial surface of the temporal lobe, is associated with an impaired ability to recognize emotions in others, which often leads to impaired social and moral reasoning.
The authors of the essay note that neuroimaging studies suggest a link between brain damage and some forms of criminal behaviour, and discuss the legal implications of these findings. They are skeptical of the use of neuroimaging data in the courtroom, and suggest that such “evidence” will only be reliable after research provides us with a better understanding of the neural correlates of criminality. They believe that advances in our understanding of brain function will eventually change our views of responsibility, free will and culpability, and could have a major impact on how the American and British legal systems treat and punish criminals. And, unlike most considerations of this topic, which have focused on the criminal, they emphasize that neuroscience also provides a possibility of gaining insight into the cognitive processes of judges and jurors, and of learning more about the limitations of eyewitness testimonies.
Mobbs, D., et al. (2007). Law, Responsibility and the Brain. PLoS Biology 5 (4) e103. doi: 10.1371/journal.pbio.0050103. [Full text]